/*
 * jchuff.c
 *
 * Copyright (C) 1991-1995, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains Huffman entropy encoding routines.
 *
 * Much of the complexity here has to do with supporting output suspension.
 * If the data destination module demands suspension, we want to be able to
 * back up to the start of the current MCU.  To do this, we copy state
 * variables into local working storage, and update them back to the
 * permanent JPEG objects only upon successful completion of an MCU.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jchuff.h"				/* Declarations shared with jcphuff.c */


/* Expanded entropy encoder object for Huffman encoding.
 *
 * The savable_state subrecord contains fields that change within an MCU,
 * but must not be updated permanently until we complete the MCU.
 */

typedef struct
{
	INT32           put_buffer;	/* current bit-accumulation buffer */
	int             put_bits;	/* # of bits now in it */
	int             last_dc_val[MAX_COMPS_IN_SCAN];	/* last DC coef for each component */
} savable_state;

/* This macro is to work around compilers with missing or broken
 * structure assignment.  You'll need to fix this code if you have
 * such a compiler and you change MAX_COMPS_IN_SCAN.
 */

#ifndef NO_STRUCT_ASSIGN
#define ASSIGN_STATE(dest,src)  ((dest) = (src))
#else
#if MAX_COMPS_IN_SCAN == 4
#define ASSIGN_STATE(dest,src)  \
	((dest).put_buffer = (src).put_buffer, \
	 (dest).put_bits = (src).put_bits, \
	 (dest).last_dc_val[0] = (src).last_dc_val[0], \
	 (dest).last_dc_val[1] = (src).last_dc_val[1], \
	 (dest).last_dc_val[2] = (src).last_dc_val[2], \
	 (dest).last_dc_val[3] = (src).last_dc_val[3])
#endif
#endif


typedef struct
{
	struct jpeg_entropy_encoder pub;	/* public fields */

	savable_state   saved;		/* Bit buffer & DC state at start of MCU */

	/* These fields are NOT loaded into local working state. */
	unsigned int    restarts_to_go;	/* MCUs left in this restart interval */
	int             next_restart_num;	/* next restart number to write (0-7) */

	/* Pointers to derived tables (these workspaces have image lifespan) */
	c_derived_tbl  *dc_derived_tbls[NUM_HUFF_TBLS];
	c_derived_tbl  *ac_derived_tbls[NUM_HUFF_TBLS];

#ifdef ENTROPY_OPT_SUPPORTED	/* Statistics tables for optimization */
	long           *dc_count_ptrs[NUM_HUFF_TBLS];
	long           *ac_count_ptrs[NUM_HUFF_TBLS];
#endif
} huff_entropy_encoder;

typedef huff_entropy_encoder *huff_entropy_ptr;

/* Working state while writing an MCU.
 * This struct contains all the fields that are needed by subroutines.
 */

typedef struct
{
	JOCTET         *next_output_byte;	/* => next byte to write in buffer */
	size_t          free_in_buffer;	/* # of byte spaces remaining in buffer */
	savable_state   cur;		/* Current bit buffer & DC state */
	j_compress_ptr  cinfo;		/* dump_buffer needs access to this */
} working_state;


/* Forward declarations */
METHODDEF boolean encode_mcu_huff JPP((j_compress_ptr cinfo, JBLOCKROW * MCU_data));
METHODDEF void finish_pass_huff JPP((j_compress_ptr cinfo));

#ifdef ENTROPY_OPT_SUPPORTED
METHODDEF boolean encode_mcu_gather JPP((j_compress_ptr cinfo, JBLOCKROW * MCU_data));
METHODDEF void finish_pass_gather JPP((j_compress_ptr cinfo));
#endif


/*
 * Initialize for a Huffman-compressed scan.
 * If gather_statistics is TRUE, we do not output anything during the scan,
 * just count the Huffman symbols used and generate Huffman code tables.
 */

METHODDEF void start_pass_huff(j_compress_ptr cinfo, boolean gather_statistics)
{
	huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
	int             ci, dctbl, actbl;
	jpeg_component_info *compptr;

	if(gather_statistics)
	{
#ifdef ENTROPY_OPT_SUPPORTED
		entropy->pub.encode_mcu = encode_mcu_gather;
		entropy->pub.finish_pass = finish_pass_gather;
#else
		ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif
	}
	else
	{
		entropy->pub.encode_mcu = encode_mcu_huff;
		entropy->pub.finish_pass = finish_pass_huff;
	}

	for(ci = 0; ci < cinfo->comps_in_scan; ci++)
	{
		compptr = cinfo->cur_comp_info[ci];
		dctbl = compptr->dc_tbl_no;
		actbl = compptr->ac_tbl_no;
		/* Make sure requested tables are present */
		/* (In gather mode, tables need not be allocated yet) */
		if(dctbl < 0 || dctbl >= NUM_HUFF_TBLS || (cinfo->dc_huff_tbl_ptrs[dctbl] == NULL && !gather_statistics))
			ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
		if(actbl < 0 || actbl >= NUM_HUFF_TBLS || (cinfo->ac_huff_tbl_ptrs[actbl] == NULL && !gather_statistics))
			ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
		if(gather_statistics)
		{
#ifdef ENTROPY_OPT_SUPPORTED
			/* Allocate and zero the statistics tables */
			/* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
			if(entropy->dc_count_ptrs[dctbl] == NULL)
				entropy->dc_count_ptrs[dctbl] = (long *)
					(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 257 * SIZEOF(long));
			MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * SIZEOF(long));

			if(entropy->ac_count_ptrs[actbl] == NULL)
				entropy->ac_count_ptrs[actbl] = (long *)
					(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 257 * SIZEOF(long));
			MEMZERO(entropy->ac_count_ptrs[actbl], 257 * SIZEOF(long));
#endif
		}
		else
		{
			/* Compute derived values for Huffman tables */
			/* We may do this more than once for a table, but it's not expensive */
			jpeg_make_c_derived_tbl(cinfo, cinfo->dc_huff_tbl_ptrs[dctbl], &entropy->dc_derived_tbls[dctbl]);
			jpeg_make_c_derived_tbl(cinfo, cinfo->ac_huff_tbl_ptrs[actbl], &entropy->ac_derived_tbls[actbl]);
		}
		/* Initialize DC predictions to 0 */
		entropy->saved.last_dc_val[ci] = 0;
	}

	/* Initialize bit buffer to empty */
	entropy->saved.put_buffer = 0;
	entropy->saved.put_bits = 0;

	/* Initialize restart stuff */
	entropy->restarts_to_go = cinfo->restart_interval;
	entropy->next_restart_num = 0;
}


/*
 * Compute the derived values for a Huffman table.
 * Note this is also used by jcphuff.c.
 */

GLOBAL void jpeg_make_c_derived_tbl(j_compress_ptr cinfo, JHUFF_TBL * htbl, c_derived_tbl ** pdtbl)
{
	c_derived_tbl  *dtbl;
	int             p, i, l, lastp, si;
	char            huffsize[257];
	unsigned int    huffcode[257];
	unsigned int    code;

	/* Allocate a workspace if we haven't already done so. */
	if(*pdtbl == NULL)
		*pdtbl = (c_derived_tbl *) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(c_derived_tbl));
	dtbl = *pdtbl;

	/* Figure C.1: make table of Huffman code length for each symbol */
	/* Note that this is in code-length order. */

	p = 0;
	for(l = 1; l <= 16; l++)
	{
		for(i = 1; i <= (int)htbl->bits[l]; i++)
			huffsize[p++] = (char)l;
	}
	huffsize[p] = 0;
	lastp = p;

	/* Figure C.2: generate the codes themselves */
	/* Note that this is in code-length order. */

	code = 0;
	si = huffsize[0];
	p = 0;
	while(huffsize[p])
	{
		while(((int)huffsize[p]) == si)
		{
			huffcode[p++] = code;
			code++;
		}
		code <<= 1;
		si++;
	}

	/* Figure C.3: generate encoding tables */
	/* These are code and size indexed by symbol value */

	/* Set any codeless symbols to have code length 0;
	 * this allows emit_bits to detect any attempt to emit such symbols.
	 */
	MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));

	for(p = 0; p < lastp; p++)
	{
		dtbl->ehufco[htbl->huffval[p]] = huffcode[p];
		dtbl->ehufsi[htbl->huffval[p]] = huffsize[p];
	}
}


/* Outputting bytes to the file */

/* Emit a byte, taking 'action' if must suspend. */
#define emit_byte(state,val,action)  \
	{ *(state)->next_output_byte++ = (JOCTET) (val);  \
	  if (--(state)->free_in_buffer == 0)  \
	    if (! dump_buffer(state))  \
	      { action; } }


LOCAL           boolean dump_buffer(working_state * state)
/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
{
	struct jpeg_destination_mgr *dest = state->cinfo->dest;

	if(!(*dest->empty_output_buffer) (state->cinfo))
		return FALSE;
	/* After a successful buffer dump, must reset buffer pointers */
	state->next_output_byte = dest->next_output_byte;
	state->free_in_buffer = dest->free_in_buffer;
	return TRUE;
}


/* Outputting bits to the file */

/* Only the right 24 bits of put_buffer are used; the valid bits are
 * left-justified in this part.  At most 16 bits can be passed to emit_bits
 * in one call, and we never retain more than 7 bits in put_buffer
 * between calls, so 24 bits are sufficient.
 */

INLINE LOCAL boolean emit_bits(working_state * state, unsigned int code, int size)
/* Emit some bits; return TRUE if successful, FALSE if must suspend */
{
	/* This routine is heavily used, so it's worth coding tightly. */
	register INT32  put_buffer = (INT32) code;
	register int    put_bits = state->cur.put_bits;

	/* if size is 0, caller used an invalid Huffman table entry */
	if(size == 0)
		ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);

	put_buffer &= (((INT32) 1) << size) - 1;	/* mask off any extra bits in code */

	put_bits += size;			/* new number of bits in buffer */

	put_buffer <<= 24 - put_bits;	/* align incoming bits */

	put_buffer |= state->cur.put_buffer;	/* and merge with old buffer contents */

	while(put_bits >= 8)
	{
		int             c = (int)((put_buffer >> 16) & 0xFF);

		emit_byte(state, c, return FALSE);
		if(c == 0xFF)
		{						/* need to stuff a zero byte? */
			emit_byte(state, 0, return FALSE);
		}
		put_buffer <<= 8;
		put_bits -= 8;
	}

	state->cur.put_buffer = put_buffer;	/* update state variables */
	state->cur.put_bits = put_bits;

	return TRUE;
}


LOCAL           boolean flush_bits(working_state * state)
{
	if(!emit_bits(state, 0x7F, 7))	/* fill any partial byte with ones */
		return FALSE;
	state->cur.put_buffer = 0;	/* and reset bit-buffer to empty */
	state->cur.put_bits = 0;
	return TRUE;
}


/* Encode a single block's worth of coefficients */

LOCAL           boolean
encode_one_block(working_state * state, JCOEFPTR block, int last_dc_val, c_derived_tbl * dctbl, c_derived_tbl * actbl)
{
	register int    temp, temp2;
	register int    nbits;
	register int    k, r, i;

	/* Encode the DC coefficient difference per section F.1.2.1 */

	temp = temp2 = block[0] - last_dc_val;

	if(temp < 0)
	{
		temp = -temp;			/* temp is abs value of input */
		/* For a negative input, want temp2 = bitwise complement of abs(input) */
		/* This code assumes we are on a two's complement machine */
		temp2--;
	}

	/* Find the number of bits needed for the magnitude of the coefficient */
	nbits = 0;
	while(temp)
	{
		nbits++;
		temp >>= 1;
	}

	/* Emit the Huffman-coded symbol for the number of bits */
	if(!emit_bits(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
		return FALSE;

	/* Emit that number of bits of the value, if positive, */
	/* or the complement of its magnitude, if negative. */
	if(nbits)					/* emit_bits rejects calls with size 0 */
		if(!emit_bits(state, (unsigned int)temp2, nbits))
			return FALSE;

	/* Encode the AC coefficients per section F.1.2.2 */

	r = 0;						/* r = run length of zeros */

	for(k = 1; k < DCTSIZE2; k++)
	{
		if((temp = block[jpeg_natural_order[k]]) == 0)
		{
			r++;
		}
		else
		{
			/* if run length > 15, must emit special run-length-16 codes (0xF0) */
			while(r > 15)
			{
				if(!emit_bits(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
					return FALSE;
				r -= 16;
			}

			temp2 = temp;
			if(temp < 0)
			{
				temp = -temp;	/* temp is abs value of input */
				/* This code assumes we are on a two's complement machine */
				temp2--;
			}

			/* Find the number of bits needed for the magnitude of the coefficient */
			nbits = 1;			/* there must be at least one 1 bit */
			while((temp >>= 1))
				nbits++;

			/* Emit Huffman symbol for run length / number of bits */
			i = (r << 4) + nbits;
			if(!emit_bits(state, actbl->ehufco[i], actbl->ehufsi[i]))
				return FALSE;

			/* Emit that number of bits of the value, if positive, */
			/* or the complement of its magnitude, if negative. */
			if(!emit_bits(state, (unsigned int)temp2, nbits))
				return FALSE;

			r = 0;
		}
	}

	/* If the last coef(s) were zero, emit an end-of-block code */
	if(r > 0)
		if(!emit_bits(state, actbl->ehufco[0], actbl->ehufsi[0]))
			return FALSE;

	return TRUE;
}


/*
 * Emit a restart marker & resynchronize predictions.
 */

LOCAL           boolean emit_restart(working_state * state, int restart_num)
{
	int             ci;

	if(!flush_bits(state))
		return FALSE;

	emit_byte(state, 0xFF, return FALSE);
	emit_byte(state, JPEG_RST0 + restart_num, return FALSE);

	/* Re-initialize DC predictions to 0 */
	for(ci = 0; ci < state->cinfo->comps_in_scan; ci++)
		state->cur.last_dc_val[ci] = 0;

	/* The restart counter is not updated until we successfully write the MCU. */

	return TRUE;
}


/*
 * Encode and output one MCU's worth of Huffman-compressed coefficients.
 */

METHODDEF       boolean encode_mcu_huff(j_compress_ptr cinfo, JBLOCKROW * MCU_data)
{
	huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
	working_state   state;
	int             blkn, ci;
	jpeg_component_info *compptr;

	/* Load up working state */
	state.next_output_byte = cinfo->dest->next_output_byte;
	state.free_in_buffer = cinfo->dest->free_in_buffer;
	ASSIGN_STATE(state.cur, entropy->saved);
	state.cinfo = cinfo;

	/* Emit restart marker if needed */
	if(cinfo->restart_interval)
	{
		if(entropy->restarts_to_go == 0)
			if(!emit_restart(&state, entropy->next_restart_num))
				return FALSE;
	}

	/* Encode the MCU data blocks */
	for(blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++)
	{
		ci = cinfo->MCU_membership[blkn];
		compptr = cinfo->cur_comp_info[ci];
		if(!encode_one_block(&state,
							 MCU_data[blkn][0], state.cur.last_dc_val[ci],
							 entropy->dc_derived_tbls[compptr->dc_tbl_no], entropy->ac_derived_tbls[compptr->ac_tbl_no]))
			return FALSE;
		/* Update last_dc_val */
		state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
	}

	/* Completed MCU, so update state */
	cinfo->dest->next_output_byte = state.next_output_byte;
	cinfo->dest->free_in_buffer = state.free_in_buffer;
	ASSIGN_STATE(entropy->saved, state.cur);

	/* Update restart-interval state too */
	if(cinfo->restart_interval)
	{
		if(entropy->restarts_to_go == 0)
		{
			entropy->restarts_to_go = cinfo->restart_interval;
			entropy->next_restart_num++;
			entropy->next_restart_num &= 7;
		}
		entropy->restarts_to_go--;
	}

	return TRUE;
}


/*
 * Finish up at the end of a Huffman-compressed scan.
 */

METHODDEF void finish_pass_huff(j_compress_ptr cinfo)
{
	huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
	working_state   state;

	/* Load up working state ... flush_bits needs it */
	state.next_output_byte = cinfo->dest->next_output_byte;
	state.free_in_buffer = cinfo->dest->free_in_buffer;
	ASSIGN_STATE(state.cur, entropy->saved);
	state.cinfo = cinfo;

	/* Flush out the last data */
	if(!flush_bits(&state))
		ERREXIT(cinfo, JERR_CANT_SUSPEND);

	/* Update state */
	cinfo->dest->next_output_byte = state.next_output_byte;
	cinfo->dest->free_in_buffer = state.free_in_buffer;
	ASSIGN_STATE(entropy->saved, state.cur);
}


/*
 * Huffman coding optimization.
 *
 * This actually is optimization, in the sense that we find the best possible
 * Huffman table(s) for the given data.  We first scan the supplied data and
 * count the number of uses of each symbol that is to be Huffman-coded.
 * (This process must agree with the code above.)  Then we build an
 * optimal Huffman coding tree for the observed counts.
 *
 * The JPEG standard requires Huffman codes to be no more than 16 bits long.
 * If some symbols have a very small but nonzero probability, the Huffman tree
 * must be adjusted to meet the code length restriction.  We currently use
 * the adjustment method suggested in the JPEG spec.  This method is *not*
 * optimal; it may not choose the best possible limited-length code.  But
 * since the symbols involved are infrequently used, it's not clear that
 * going to extra trouble is worthwhile.
 */

#ifdef ENTROPY_OPT_SUPPORTED


/* Process a single block's worth of coefficients */

LOCAL void htest_one_block(JCOEFPTR block, int last_dc_val, long dc_counts[], long ac_counts[])
{
	register int    temp;
	register int    nbits;
	register int    k, r;

	/* Encode the DC coefficient difference per section F.1.2.1 */

	temp = block[0] - last_dc_val;
	if(temp < 0)
		temp = -temp;

	/* Find the number of bits needed for the magnitude of the coefficient */
	nbits = 0;
	while(temp)
	{
		nbits++;
		temp >>= 1;
	}

	/* Count the Huffman symbol for the number of bits */
	dc_counts[nbits]++;

	/* Encode the AC coefficients per section F.1.2.2 */

	r = 0;						/* r = run length of zeros */

	for(k = 1; k < DCTSIZE2; k++)
	{
		if((temp = block[jpeg_natural_order[k]]) == 0)
		{
			r++;
		}
		else
		{
			/* if run length > 15, must emit special run-length-16 codes (0xF0) */
			while(r > 15)
			{
				ac_counts[0xF0]++;
				r -= 16;
			}

			/* Find the number of bits needed for the magnitude of the coefficient */
			if(temp < 0)
				temp = -temp;

			/* Find the number of bits needed for the magnitude of the coefficient */
			nbits = 1;			/* there must be at least one 1 bit */
			while((temp >>= 1))
				nbits++;

			/* Count Huffman symbol for run length / number of bits */
			ac_counts[(r << 4) + nbits]++;

			r = 0;
		}
	}

	/* If the last coef(s) were zero, emit an end-of-block code */
	if(r > 0)
		ac_counts[0]++;
}


/*
 * Trial-encode one MCU's worth of Huffman-compressed coefficients.
 * No data is actually output, so no suspension return is possible.
 */

METHODDEF       boolean encode_mcu_gather(j_compress_ptr cinfo, JBLOCKROW * MCU_data)
{
	huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
	int             blkn, ci;
	jpeg_component_info *compptr;

	/* Take care of restart intervals if needed */
	if(cinfo->restart_interval)
	{
		if(entropy->restarts_to_go == 0)
		{
			/* Re-initialize DC predictions to 0 */
			for(ci = 0; ci < cinfo->comps_in_scan; ci++)
				entropy->saved.last_dc_val[ci] = 0;
			/* Update restart state */
			entropy->restarts_to_go = cinfo->restart_interval;
		}
		entropy->restarts_to_go--;
	}

	for(blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++)
	{
		ci = cinfo->MCU_membership[blkn];
		compptr = cinfo->cur_comp_info[ci];
		htest_one_block(MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
						entropy->dc_count_ptrs[compptr->dc_tbl_no], entropy->ac_count_ptrs[compptr->ac_tbl_no]);
		entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
	}

	return TRUE;
}


/*
 * Generate the optimal coding for the given counts, fill htbl.
 * Note this is also used by jcphuff.c.
 */

GLOBAL void jpeg_gen_optimal_table(j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[])
{
#define MAX_CLEN 32				/* assumed maximum initial code length */
	UINT8           bits[MAX_CLEN + 1];	/* bits[k] = # of symbols with code length k */
	int             codesize[257];	/* codesize[k] = code length of symbol k */
	int             others[257];	/* next symbol in current branch of tree */
	int             c1, c2;
	int             p, i, j;
	long            v;

	/* This algorithm is explained in section K.2 of the JPEG standard */

	MEMZERO(bits, SIZEOF(bits));
	MEMZERO(codesize, SIZEOF(codesize));
	for(i = 0; i < 257; i++)
		others[i] = -1;			/* init links to empty */

	freq[256] = 1;				/* make sure there is a nonzero count */
	/* Including the pseudo-symbol 256 in the Huffman procedure guarantees
	 * that no real symbol is given code-value of all ones, because 256
	 * will be placed in the largest codeword category.
	 */

	/* Huffman's basic algorithm to assign optimal code lengths to symbols */

	for(;;)
	{
		/* Find the smallest nonzero frequency, set c1 = its symbol */
		/* In case of ties, take the larger symbol number */
		c1 = -1;
		v = 1000000000L;
		for(i = 0; i <= 256; i++)
		{
			if(freq[i] && freq[i] <= v)
			{
				v = freq[i];
				c1 = i;
			}
		}

		/* Find the next smallest nonzero frequency, set c2 = its symbol */
		/* In case of ties, take the larger symbol number */
		c2 = -1;
		v = 1000000000L;
		for(i = 0; i <= 256; i++)
		{
			if(freq[i] && freq[i] <= v && i != c1)
			{
				v = freq[i];
				c2 = i;
			}
		}

		/* Done if we've merged everything into one frequency */
		if(c2 < 0)
			break;

		/* Else merge the two counts/trees */
		freq[c1] += freq[c2];
		freq[c2] = 0;

		/* Increment the codesize of everything in c1's tree branch */
		codesize[c1]++;
		while(others[c1] >= 0)
		{
			c1 = others[c1];
			codesize[c1]++;
		}

		others[c1] = c2;		/* chain c2 onto c1's tree branch */

		/* Increment the codesize of everything in c2's tree branch */
		codesize[c2]++;
		while(others[c2] >= 0)
		{
			c2 = others[c2];
			codesize[c2]++;
		}
	}

	/* Now count the number of symbols of each code length */
	for(i = 0; i <= 256; i++)
	{
		if(codesize[i])
		{
			/* The JPEG standard seems to think that this can't happen, */
			/* but I'm paranoid... */
			if(codesize[i] > MAX_CLEN)
				ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);

			bits[codesize[i]]++;
		}
	}

	/* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure
	 * Huffman procedure assigned any such lengths, we must adjust the coding.
	 * Here is what the JPEG spec says about how this next bit works:
	 * Since symbols are paired for the longest Huffman code, the symbols are
	 * removed from this length category two at a time.  The prefix for the pair
	 * (which is one bit shorter) is allocated to one of the pair; then,
	 * skipping the BITS entry for that prefix length, a code word from the next
	 * shortest nonzero BITS entry is converted into a prefix for two code words
	 * one bit longer.
	 */

	for(i = MAX_CLEN; i > 16; i--)
	{
		while(bits[i] > 0)
		{
			j = i - 2;			/* find length of new prefix to be used */
			while(bits[j] == 0)
				j--;

			bits[i] -= 2;		/* remove two symbols */
			bits[i - 1]++;		/* one goes in this length */
			bits[j + 1] += 2;	/* two new symbols in this length */
			bits[j]--;			/* symbol of this length is now a prefix */
		}
	}

	/* Remove the count for the pseudo-symbol 256 from the largest codelength */
	while(bits[i] == 0)			/* find largest codelength still in use */
		i--;
	bits[i]--;

	/* Return final symbol counts (only for lengths 0..16) */
	MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits));

	/* Return a list of the symbols sorted by code length */
	/* It's not real clear to me why we don't need to consider the codelength
	 * changes made above, but the JPEG spec seems to think this works.
	 */
	p = 0;
	for(i = 1; i <= MAX_CLEN; i++)
	{
		for(j = 0; j <= 255; j++)
		{
			if(codesize[j] == i)
			{
				htbl->huffval[p] = (UINT8) j;
				p++;
			}
		}
	}

	/* Set sent_table FALSE so updated table will be written to JPEG file. */
	htbl->sent_table = FALSE;
}


/*
 * Finish up a statistics-gathering pass and create the new Huffman tables.
 */

METHODDEF void finish_pass_gather(j_compress_ptr cinfo)
{
	huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
	int             ci, dctbl, actbl;
	jpeg_component_info *compptr;
	JHUFF_TBL     **htblptr;
	boolean         did_dc[NUM_HUFF_TBLS];
	boolean         did_ac[NUM_HUFF_TBLS];

	/* It's important not to apply jpeg_gen_optimal_table more than once
	 * per table, because it clobbers the input frequency counts!
	 */
	MEMZERO(did_dc, SIZEOF(did_dc));
	MEMZERO(did_ac, SIZEOF(did_ac));

	for(ci = 0; ci < cinfo->comps_in_scan; ci++)
	{
		compptr = cinfo->cur_comp_info[ci];
		dctbl = compptr->dc_tbl_no;
		actbl = compptr->ac_tbl_no;
		if(!did_dc[dctbl])
		{
			htblptr = &cinfo->dc_huff_tbl_ptrs[dctbl];
			if(*htblptr == NULL)
				*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
			jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]);
			did_dc[dctbl] = TRUE;
		}
		if(!did_ac[actbl])
		{
			htblptr = &cinfo->ac_huff_tbl_ptrs[actbl];
			if(*htblptr == NULL)
				*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
			jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]);
			did_ac[actbl] = TRUE;
		}
	}
}


#endif							/* ENTROPY_OPT_SUPPORTED */


/*
 * Module initialization routine for Huffman entropy encoding.
 */

GLOBAL void jinit_huff_encoder(j_compress_ptr cinfo)
{
	huff_entropy_ptr entropy;
	int             i;

	entropy = (huff_entropy_ptr) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(huff_entropy_encoder));
	cinfo->entropy = (struct jpeg_entropy_encoder *)entropy;
	entropy->pub.start_pass = start_pass_huff;

	/* Mark tables unallocated */
	for(i = 0; i < NUM_HUFF_TBLS; i++)
	{
		entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
#ifdef ENTROPY_OPT_SUPPORTED
		entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
#endif
	}
}
